Unexamined Japanese Patent Publication No. 2005-130292 discloses one of conventional antenna devices. This one is a balanced antenna detailed hereinafter with reference to FIG. 9.
Conventional antenna device 1 shown in FIG. 9 comprises the following elements:                (1) grounding subject 2;        (2) feeder 3 insulated from grounding subject 2;        (3) first feeding line 4 and second feeding line 5 both extending from feeder 3 along the direction leaving away from grounding subject 2;        (4) first conductor 7 shaping like a looped triangle and coupled to first feeding line 4 at first feeder top 6; and        (5) second conductor 9 coupled to second feeding line 5 at second feeder top 8.First conductor 7 and second conductor 9 are symmetrically placed with respect to a phantom line extending through feeder 3.        
First conductor 7 is formed of the following elements:                (4-1) first side 10 extending from first feeder top 6 toward the outside of antenna device 1 while approaching grounding subject 2;        (4-2) second side 11 extending from first feeder top 6 toward the outside of antenna device 1 while leaving away from grounding subject 2 further than first side 10; and        (4-3) third side 12 coupled to the second end of first side 10 as well as the second end of second side 11. (the first ends of first side 10 and second side 11 are respectively coupled to first feeder top 6)Second conductor 9 is formed of the following elements similarly to the first conductor 7:        (5-1) first side 13 extending from second feeder top 8 toward the outside of antenna device 1 while approaching grounding subject 2;        (5-2) second side 14 extending from second feeder top 8 toward the outside of antenna device 1 while leaving away from grounding subject 2 further than first side 14; and        (5-3) third side 15 coupled to the second end of first side 13 as well as the second end of second side 14. (the first ends of first side 13 and second side 14 are respectively coupled to second feeder top 8)        
First side 10 of first conductor 7 and the other first side 13 of second conductor 9, both of which are placed nearest to grounding subject 2 among other sides, approach grounding subject 2 while they extend toward the outside of antenna device 1. Since the electric field becomes higher as first sides 10 and 13 run further toward the outside of antenna device 1, first sides 10 and 13 are electro-magnetically coupled to grounding subject 2, so that the reflecting function of grounding subject 2 is obliged to lower. As a result, the directionality of the antenna device along the direction further away from grounding subject 2, namely, the directionality along the upward direction (along allow mark A) in FIG. 9 lowers.
Unexamined Japanese Patent Publication No. S62-31204 discloses another conventional antenna device. This one is a dipole antenna described hereinafter with reference to FIG. 10. Conventional antenna device 100 shown in FIG. 10 comprises the following elements:                (1) feeder 101;        (2) first conductor 102 coupled to feeder 101; and        (3) second conductor 103 symmetrically disposed to first conductor 102 with respect to a phantom line extending through feeder 101.        
First conductor 102 is formed of the following elements:                (2-1) first side 107 coupled to feeder 101 at its first end; and        (2-2) first base 108 coupled substantially vertically to the second end of first side 107.        
Second conductor 103 is formed of the following elements similarly to the first conductor 102:                (3-1) second side 113 coupled to feeder 101 at its first end; and        (3-2) second base 114 coupled substantially vertically to the second end of second side 113.First side 107 is generally in parallel with second side 113.        
Antenna device 100 discussed above, however, has only first base 108 and second base 114 as antenna elements for contributing to radiation, so that the antenna fractional bandwidth becomes narrow.